1. Field of the Invention
The invention relates to a method for initializing data, particularly seismic data, acquisition apparatus and a device for implementing same.
The method and device of the invention apply in particular to the initialization of seismic data acquisition apparatus such as they are used in present day seismic prospection systems. A very large number of geophones or hydrophones are disposed along the seismic profile to be studied.
These sensors, which may be distributed over lengths of several kilometers, are associated with acquisition apparatus. Seismic waves having been transmitted into the ground, the waves reflected by the different subterranean discontinuities are received by means of the sensors. The signals picked up are collected, digitized and stored in the acquisition apparatus. Once the reception and recording cycle is finished, a seismic laboratory centralizes all the data by sequentially ordering all the acquisition apparatus to transmit to it those which have been respectively collected. The transmission may take place over a transmission cable connecting all the acquisition apparatus to the seismic laboratory or else by short wave link.
2. Description of the Prior Art
A mixed short wave link or cable transmission system is described in the publsihed French patent applications n.degree.2 511 772 and 2 538 561 and in the French patent application EN 86/07930. It is adapted to acquisition apparatus arranged for receiving orders from a central control and recording system and for transmitting data thereto by a radio, unless a transmission cable is connected to them. In this case, the radio transmission-reception means are automatically switched off, the orders and the data being exchanged through the transmission cable. The acquisition apparatus and their particular transmission means are disposed in sealed cases possibly associated with buoys, which are deposited on the ground, at a certain distance from each other and connected to the seismic receivers. They are well adapted to collecting data during seismic prospection operations carried out in difficult zones, whether they are very humid zones: lakes, marshes, etc, zones whose relief and/or vegetation make short wave link transmissions problematical, or zones where the regulations concerning radio-transmission are very restrictive. One or more relay stations disposed between the central laboratory and directly inacessible cases or buoys may be used for facilitating centralization of the seismic data.
The different acquisition cases fulfill very complex functions, whether from the point of view of seismic data acquisition or transmission thereof to the central laboratory. The data coming from the sensors are first of all amplified and filtered. Then they are sampled and digitized before being stored. The result obtained by the acquisition chain depends on the frequency of sampling the data, and on the characteristics of the low pass and high pass electronic filters which it comprises. With the recording cycle terminated, orders and data relative to a case are very often transferred over a short wave link. The frequency of the radio carrier used depends on the local telecommunications regulations and also on the position of the case in the seismic reception system disposed on the ground. Depending on whether the case may be reached directly from the central short wave link connection station or else can only be reached through a relay station, the communication frequency may be different.
The great variety of operating conditions to which a seismic reception system must correspond make necessary the use of readily adaptable acquisition cases. The introduction of the initial conditions must be able to be carried out after positioning of the cases, in the very position where they are located, under optimum conditions of reliability and rapidity.
Initialization of the acquisition cases is easy on dry land. One or more operators provided with control boxes go to the site, to the very place at which acquistion cases are installed. Each of the cases is provided with a readily accessible socket which the operator frees for connecting thereto a cable connected to his initialization box.
It is quite different when the seismic reception and transmission system is installed in difficult regions. This is more particularly the case in marshy zones where very often the buoys supporting the cases can only be reached by boat. The effective connection of a control box by cable to each acquisition case is made more complicated because of the sealing devices protecting the electronic circuits and their access zones from water.
The method of the invention allows the rapid initialization of acquisition cases each adapted for collecting signals delivered by sensors, processing them and recording them and, on a control from a central laboratory, transferring thereto the data relative to said signals, following a given transmission channel.